public int kSmallest(int k) {
			
			return kSmallest(k-1, 0, num.length-1);
			}
			private int kSmallest(int k, int left, int right){
				int rtn;
				int pivot;
				int pivotIndex;
				
				if (right <= left)
					rtn = num[left];
				else {//partition
				  
					pivot = num[(int)     Math.random()*(right-left)+left];
					pivotIndex = partition(pivot, left, right);
					System.out.println("pivot = "+ pivot);
						
			
				if (k < pivotIndex)
				kSmallest(k, left, pivotIndex-1);
				else
					kSmallest(k, pivotIndex+1, right );
				
				rtn = num[k];
				}
				
				return rtn;
			
			}

			private int partition(int pivot, int left, int right){
			
				while (left < right){
					while (num[left] < pivot) left++;
					while (num[right] > pivot) right--;
					exch(left,right);
				}
			return left;
			}
			private void exch( int i, int j) {
		     
		        int swap = num[i];
		        num[i] = num[j];
		        num[j] = swap;
		    }